This is an open label, single dose design study which will evaluate the disposition of famotidine in two groups of patients. Group 1 (18 patients) will consist of patients with acute renal insufficiency and group 2 (18 patients) will consist of patients with chronic renal insufficiency. Patients in group 1 will be hospitalized patients with a renal insufficiency secondary to an acute process such as sepsis, while patients in group 2 will have stable, reduced renal function for a period of three months prior to study entry and may be either inpatients or outpatients. Prior to entry into the study, patients will receive a complete physical examination, a serum or urine pregnancy test for females of childbearing potential, and clinical laboratories. Each group of patients will be stratified into three subgroups according to the severity of renal insufficiency. The length of study participation will vary according to the severity of renal insufficiency so that patients with mild renal insufficiency will participate for 72 hours. The 48 hour and 72 hour samples will be optional for outpatients in the group 2 (chronic renal insufficiency group). Patients in group 1 with a low intragastric pH by gastric pH aspiration will undergo a pharmacodynamic analysis of famotidine by use of intragastric pH measurement. The pharmacodynamic analysis in group 2 patients will be optional as the majority of these patients will be outpatients. To monitor intragastric pH in patients with an intragastric pH #4 by a pH meter, an Accusite pHR nasogastric tube will be placed using standard techniques, prior to famotidine administration. pH readings will be recorded prior to the famotidine administration, every five minutes during the famotidine infusion and periodically up to 72 hrs. Following collection of a baseline urine sample and a predose blood sample, a single intravenous dose of famotidine will be administered via constant rate infusion over a 15 minute period to study subjects. Samples will be obtained at specific time points for measurement of famotidine. Serum creatinines obtained in the routine clinical management of the patient will be recorded. Timed, quantitative collections of urine will also be obtained over the post-dose periods.